At which layer of the OSI model does the protocol that provides the information that is displayed
by the show cdp neighbors command operate?

A.
application

B.
transport

C.
network

D.
physical

E.
data link

Explanation:
Explanation/Reference:
http://computernetworkingnotes.com/cisco-devices-administration-and-configuration/ciscodiscoveryprotocol.html
CDP is a device discovery protocol that runs over Layer 2 (the data link layer) on all Ciscomanufactured devices (routers, bridges, access servers, and switches) and allows network
management applications to discover Cisco devices that are neighbors of already known devices.
With CDP, network management applications can learn the device type and the Simple Network
Management Protocol (SNMP) agent address of neighboring devices running lower-layer,
transparent protocols.
CDP allows devices to share basic configuration information without even configuring any protocol
specific information and is enabled by default on all interfaces.
CDP is a Datalink Protocol occurring at Layer 2 of the OSI model.
CDP is not routable and can only go over to directly connected devices.
CDP is enabled, by default, on all Cisco devices. CDP updates are generated as multicasts every
60 seconds with a hold-down period of 180 seconds for a missing neighbor. The no cdp run
command globally disables CDP, while the no cdp enable command disables CDP on an
interface. Use show cdp neighbors to list out your directly connected Cisco neighboring devices.
Adding the detail parameter will display the layer-3 addressing configured on the neighbor.